This is a little bit of a stretch, and not always true. Clayton left Franklin to take the Hillsboro job and went to the state within 2 years of being there. Jay Gore was at Brentwood for some time before going to McGavock. I think opportunity is there from both outside MNPS and from within to hire quality coaches.
The issue is the academic part someone mentioned a few posts prior. MNPS ranks exceptionally low in comparison to other counties across multiple academic levels (reading comprehension, test scores, etc). Raise the academic level in the district, and in turn raise the athletic level as well. Why? Because more Metro-Davidson families will choose to send their kids to their local school, instead of a private/charter school.